This invention relates to a layer-thickness meter for measuring the thickness of non-magnetic layers upon ferromagnetic substrates, in which the force of adhesion to the layer being measured of a permanent magnet arranged for rotation upon a balanced lever arm is a measure of the layer thickness and is measured by means of a spring which is stressed by the rotation of a graduated scale disc that co-operates with an index mark on the housing of the meter.
In a known thickness meter of this type, as shown in U.S. Pat. No. 3,521,160, granted to Hans Nix and Erich Steingroever July 21, 1970, a spread arises in the measured values of layer thickness merely from the reason that it is difficult to arrest the movement of the graduated scale disc exactly at the instant of its rotation at which the permanent magnet is raised. Since the reaction time of the operator employing the meter is not always the same, there arise multiple measurement deviations of the measured value which in previously known apparatus could not be eliminated in a simple manner.
An attempt to solve this problem by the inclusion of a pivotally mounted pawl or a friction brake actuated by the balanced arm, to stop the rotation of the graduated scale when the magnet is lifted up from the layer being measured is disclosed in U.S. Pat. No. 4,152,646 granted to Erich A. Steingroever and Hans E. Nix on May 1, 1979 and assigned to the assignee of this application. In this patent, the friction brake can be overcome if excessive force is exerted on the rotary scale, and the pawl mechanism, being actuated by a spring member in contact with the balanced arm sometimes introduces a delay in this actuation.